Optical distance measurement devices are known, which can ascertain a distance between the distance measurement device and a target object. For this purpose, the distance measurement devices emit a light beam in the direction of the target object and detect light which is reflected from the object and returns in the direction of the distance measurement device.
The ascertainment of the distance can be performed by means of a runtime method, also referred to as a time-of-flight method. The measurement can occur in the time range or in the frequency range in this case. In the case of a chronological measurement, for example, a short laser pulse can be emitted at a point in time tstart toward the target object and scattered or reflected thereon. A part of this measurement radiation arrives at the optical receiver, for example, via a receiving optical system and reaches the receiver at a point in time tstop. The distance d of the target object is calculated from the measured runtime (tstop−tstart) and the speed of light c0.
In the case of a measurement in the frequency range or according to the phase runtime method, the optical radiation of a light source can be modulated in a sinusoidal manner in its intensity, for example. This modulated radiation is emitted toward the target object and scattered or reflected thereon. A part of the reflected radiation arrives at an optical receiver, for example, via a receiving optical system. As a function of a distance to the target object, the received sinusoidal intensity-modulated radiation has a phase offset to the emitted sinusoidal intensity-modulated signal. The distance to the target object can be calculated from the phase difference between received and emitted signal, the known modulation frequency, and the speed of light. Alternatively to the sinusoidal intensity modulation mentioned as an example, square-wave pulses and other modulation forms can be selected. Ambiguities in the assignment of a distance to a phase can be resolved by measurements at multiple closely adjacent frequencies. The measurement precision of the above-described distance measurement devices is not always satisfactory, however.